The present invention relates to an insulation state detector which detects a ground fault or an insulation state with respect to a ground potential portion of a DC power source on the basis of a charging voltage of a flying capacitor charged by a DC power source insulated from the ground potential portion.
For example, in a vehicle which uses electric power as energy for propulsion, it is common to insulate a high-voltage (for example, 200 V) DC power source from the vehicle body. In addition, as an insulation state detector which detects a ground fault or an insulation state with respect to a ground potential portion of such a DC power source, a device that uses a flying capacitor charged by the DC power source is known in the related art. This kind of insulation state detector detects a ground fault or an insulation state of the DC power source by charging the flying capacitor with a charging voltage corresponding to the voltage of the DC power source or with a charging voltage corresponding to a ground fault resistor on the positive or negative side and measuring the charging voltage using a measuring unit, such as a microcomputer (for example, Patent Document 1).